The concept of an axon reflex has long been a description of a physiological phenomenon present in skin in which sensory neurons have both afferent and efferent functions. It has been suggested that action potentials generated by the afferent terminal travel toward both the central nervous system and also toward the periphery, participating in local inflammatory processes including vasodilatation and mast cell degranulation. However, the exact nature of this interesting and important phenomenon has yet to be ascertained. For example, it is possible that the afferent and efferent limbs are not specialized as originally hypothesized. A physiological and morphological study on the interface between the characterized nerve terminal and its surrounding structure will provide further insight on this issue. Because mast cell degranulation and vasomotor modulation are linked to chronic and acute disease, the results of these experiments will be of clinical, as well as, theoretical interest. These experiments are difficult to perform in the skin. A different preparation, splanchnic nerve - mesenteric membrane in vivo and in vitro preparation, is likely to provide important information about the nature of the axon reflex. The mesentery is translucent, allowing the visualization of both nerve fiber and its possible target structure and is permeable to vital dyes, peptide agonists and antagonists, and pharmacological and biological agents. A combination of single unit recording (in which the functional location of nerve terminals can be defined by adequate stimuli), and the use of vital dyes to stain the nerve terminals, and with the aid of video imaging system to record the nerve terminal and its vicinity tissue structure, will enable an investigation of the precise nature of the axon reflex mechanism.